A related art process cartridge has been known which includes an image carrier cartridge having a photosensitive drum (image carrier), a developing cartridge having a developing roller (developer carrier) and an image forming unit case to which the image carrier cartridge and the developing cartridge are detachably mounted. According to this technology, the image forming unit case is provided therein with three rollers that support the developing cartridge and a press member that presses the developing cartridge so as to depress the developing roller to the photosensitive drum.
In addition, the developing cartridge is provided with a driving input part to which external power for rotating the developing roller is input. Two of the three rollers are arranged at a photosensitive drum side rather than a rotational axis line of the driving input part and the other one roller is arranged at an opposite side to the two rollers with the rotational axis line being interposed therebetween.